That a significant fraction of the meat butchered in the United States, not to mention the world, is tenderized by one method or the other, prior to being sold, is no longer even a poorly kept secret. Today, throughout the world, meat is routinely tenderized prior to being placed on the shelves for purchase by the consumer. By far the most desirable means for tenderizing meat is by natural aging but this process is too expensive except for the most choice cuts. For average quality meat, less expensive methods are favored, such as the use of various chemicals, vegetable enzymes and the like, the effectiveness of which appears to be correlatable with the amount used, with a predictable effect on the taste of the end product. Presently most favored are tenderizing machines which perform the tenderizing function by cutting sinews and fibers of the meat. This cutting is usually effected by arrow-shaped knife edges on a long slender knife shaft. When it can be reasonably assumed that the meat will be free of knife edge-damaging material, then the meat may be tenderized with the knives rigidly mounted. However, when there is reason to expect that pieces of bone, gristle and the like may be included in the meat to be tenderized, it is provident to mount the knives in such a manner that they are less likely to be broken or damaged by tough masses within the meat which masses have the effect of retarding the movement of the knives.
A representative meat tenderizer utilizing rigidly mounted knife blades is disclosed in U.S. Pat. No. 3,744,089 to Fred Fetzer, et al, which also teaches a stripper carriage constructed to move in coordination with a ram carriage. Locking pawls carried by the stripper carriage are locked relative to the frame of the machine before the ram starts to withdraw the tenderizing knives out of the meat. When the knives are withdrawn from the meat, the locking pawls are released and then the stripper carriage moves upwardly with the ram carriage. The locking pawls and related mechanism is a mechanical locking means for controlling the operation of the stripper.
It should be noted that Fetzer et al teaches using a conveyor belt which is driven to produce a predetermined amount of movement; and this conveyor movement and timing means which causes the conveyor belt to move only when the knives are clear of the meat, may be satisfactorily used with my apparatus. Conveyor means, other than of the type which provides incremental advance may also be used. For example, a conveyor having a continuous movement so that meat pieces travelling thereon can be knifed thereon, is taught in U.S. Pat. No. 3,719,504 to Joseph Greenspan et al, and may also be adapted for use with my invention. In any event, the particular manner of presenting the meat to be tenderized beneath the knives of my invention is a matter of choice and may be manual or mechanical, utilizing any known means to serve the purpose. A further description of means for presenting the meat beneath the knives is unnecessary as it forms no part of the present invention.
A meat tenderizer, utilizing a constant fluid-pressure to cushion a multiplicity of tenderizing knives is disclosed in U.S. Pat. No. 3,535,734 to Henry M. Ross. After dwelling on the problems of tenderizing meat, there is presented a carefully detailed analysis of the problems associated with the use of spring-biased knives. Ross also states that the piercing action of spring-biased spikes or knives "tends either to alter the shape of the meat in much the fashion of cube steak hammers . . . , or to be ineffective in breaking down the tough fiber structure." This latter problem is not evident in my invention in which slender knives are preferably used.
It is further stated in Ross that "A spring rate system, which is not a force limiting system, cannot result in a practical answer." Accordingly, the Ross patent provides a reciprocable fluid reservoir which exerts a constant fluid pressure selected to be less than one-half of the force required to damage a knife, providing a safety factor in excess of 2. When this force is exceeded the shank of the knife is pushed back into the pressure head, against the force exerted by the fluid. Since the force exerted by the fluid is constant, there is no total release. As the reservoir is raised enough to withdraw the knives from the meat, the constant fluid pressure in the reservoir forces the retracted shank out of the reservoir. Like Ross, U.S. Pat. No. 3,381,603 discloses a fluid pressurized force yieldable needle.
The use of a spring-biased system is unequivocally abjured because the problems of mechanical meat tenderizing "can be solved practically only by a true force-limiting system and not by a spring-biased (spring rate) system which is, in fact, an increasing-force system, since, in a spring rate system, the force will increase as the blade is forced to retract as a natural consequence of Hooke's Law". Yet, it is a spring-biased system which is used in my invention in a unique and surprisingly effective embodiment to be described hereinafter.